Organic electroluminescent device and method of fabricating the same

ABSTRACT

An organic electroluminescent device including a driving element having a driving gate electrode connected to the switching element, the driving gate electrode formed uniformly on the substrate, a driving source electrode having a first driving source electrode along a first direction and a plurality of second driving source electrodes extending from the first driving source electrode along a second direction crossing the first direction, a driving drain electrode spaced apart from the driving source electrode, the driving drain electrode having a first driving drain electrode along the first direction and a plurality of second driving drain electrodes extending from the first driving drain electrode along the second direction, wherein the plurality of second driving source electrodes alternate with the plurality of second driving drain electrodes, wherein the driving source electrode and the driving drain electrode including an interval therebetween are facing the driving gate electrode.

This application is a Divisional of Copending U.S. patent applicationSer. No. 11/154,980 filed Jun. 17, 2005, and claims benefit of KoreanPatent Application No. 2004-062689 filed Aug. 10, 2004, which are herebyincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electroluminescent deviceand more particularly, to an active matrix organic electroluminescentdevice and a method of fabricating the same.

2. Discussion of the Related Art

In general, an organic electroluminescent device (OLED) emits light byinjecting electrons from a cathode and holes from an anode into anemission layer, combining the electrons with the holes, generating anexciton, and transitioning the exciton from an excited state to a groundstate. Compared to a liquid crystal display (LCD) device, an additionallight source is not necessary for the OLED to emit light because thetransition of the exciton between the two states causes light to beemitted. Accordingly, the size and weight of the OLED can be reduced.The OLED has other excellent characteristics such as low powerconsumption, superior brightness, and fast response time. Because ofthese characteristics, the OLED is a promising display fornext-generation consumer electronic applications such as cellularphones, car navigation systems (CNS), personal digital assistants (PDA),camcorners, and palmtop computers. Moreover, since fabricating the OLEDis a simple process with a few processing steps, an OLED is cheaper toproduce than a LCD device.

Two different types of OLEDs exist: passive matrix and active matrix.While both the passive matrix OLED and the active matrix OLED have asimple structure and are formed by a simple fabricating process, thepassive matrix OLED requires a relatively high amount of power tooperate. In addition, the display size of a passive matrix OLED islimited by its structure. Furthermore, as the number of conductive linesincreases, the aperture ratio of a passive matrix OLED decreases. Incontrast, active matrix OLEDs are highly efficient and can produce ahigh-quality image for a large display with relatively low power.

FIG. 1 is a schematic cross-sectional view of an OLED according to arelated art. In FIG. 1, an array element 14 including a thin filmtransistor (TFT) T is formed on a first substrate 12. A first electrode16, an organic electroluminescent layer 18, and a second electrode 20are formed over the array element 14. The organic electroluminescentlayer 18 may separately display red, green, and blue colors for eachpixel region. A second substrate 28 faces the first substrate 12 and isspaced apart from the first substrate 12.

The first and the second substrates 12 and 28 are attached to each otherwith a sealant 26. The OLED is encapsulated by attaching the firstsubstrate 12 to the second substrate 28. The second substrate 28includes a moisture absorbent material 22 to eliminate moisture andoxygen that may penetrate into a capsule of the organicelectroluminescent layer 18. After etching a portion of the secondsubstrate 28, the etched portion is filled with the moisture absorbentmaterial 22 and the filled moisture absorbent material is fixed by aholding element 25.

FIG. 2 is an equivalent circuit diagram of the OLED according to therelated art. In FIG. 2, a gate line 36 crosses a data line 49, and aswitching element T_(S) at a crossing of the gate line 36 and the dataline 49 is connected to the gate line 36 and the data line 49. A drivingelement T_(D) electrically connects the switching element T_(S) to anorganic electroluminescent diode D_(EL). A storage capacitor C_(ST) isformed between a driving gate electrode 34 and a driving sourceelectrode 52 of the driving element T_(D), as the driving element T_(D)is a positive type transistor. The organic electroluminescent diodeD_(EL) is connected to a power line 62, and the driving drain electrodemay be connected to an anode of the organic electroluminescent diodeD_(EL).

When a scan signal of the gate line 36 is applied to a switching gateelectrode 32 of the switching element T_(S), an image signal of the dataline 49 is applied to the driving gate electrode 34 of the drivingelement T_(D) through the switching element T_(S). The current densityof the driving element T_(D) is modulated by the image signal applied tothe driving gate electrode 34. As a result, the organicelectroluminescent diode D_(EL) can display images with gray scalelevels. Moreover, because the image signal stored in the storagecapacitor C_(ST) is applied to the driving gate electrode 34, thecurrent density flowing into the organic electroluminescent diode D_(EL)is uniformly maintained until the next image signal is applied, evenwhen the switching element T_(S) is turned off. The switching elementT_(S) and the driving element T_(D) can be a polycrystalline silicon TFTor an amorphous silicon TFT. The process of fabricating an amorphoussilicon TFT is simpler than the process for a polycrystalline siliconTFT.

FIG. 3 is a schematic cross-sectional view illustrating a switchingelement and a driving element including an amorphous TFT for one pixelregion of an OLED according to the related art. In FIG. 3, a gate line36 is formed on a substrate 30 in a first direction, a data line 49crosses the gate line 36 in a second direction to define a pixel regionP, and a power line 62 is arranged in parallel to the data line 49 andcrosses the gate line 36. A switching element T_(S) adjacent to thepixel region P is connected to the gate and data lines 36 and 49. Adriving element T_(D) is connected to the switching element T_(S). Inaddition, the switching element T_(S) includes switching gate electrode32, switching semiconductor layer 56, switching source electrode anddrain electrode 48 and 50. The driving element T_(D) includes a drivinggate electrode 34, a driving semiconductor layer 58, a driving sourceelectrode and a driving drain electrode 52 and 54. Specifically, thedriving gate electrode 34 is connected to the switching drain electrode50, the driving source electrode 52 is connected to the power line 62,and the driving drain electrode 54 is connected to a first electrode 66of the organic electroluminescent diode D_(EL) (of FIG. 2). Theswitching semiconductor layer 56 and the driving semiconductor layer 58may be formed of amorphous silicon.

The amorphous silicon driving TFT should have a large width to lengthratio (W/L ratio) in order to drive the organic electroluminescent diodeD_(EL) (of FIG. 2). In this case, a size of the driving element T_(D) ismuch larger than a size of the switching element T_(S) in order tosupply enough current to the organic electroluminescent diode D_(EL).

Accordingly, to obtain a large width to length ratio (W/L ratio), thedriving source electrode and drain electrode 52 and 54 include firstdriving source electrode and drain electrode 52 a and 54 a along thefirst direction, and second driving source electrode and drain electrode52 b and 54 b extending from the first driving source electrode anddrain electrode 52 a and 54 a along the second direction such as afinger shape, respectively. Here, the second driving source electrode 52b alternates with the second driving drain electrode 54 b.

FIG. 4 is a schematic plan view showing a driving element of an OLEDaccording to a first example of the related art.

In FIG. 4, a driving element T_(D) includes a driving gate electrode 34,a driving semiconductor layer 58 over the driving gate electrode 34, adriving source electrode 52 on the driving semiconductor layer 58 and adriving drain electrode 54 spaced apart from the driving sourceelectrode 52 on the driving semiconductor layer 58. Although not shown,the driving semiconductor layer 58 includes a driving active layer of anintrinsic amorphous silicon and a driving ohmic contact layer of a dopedamorphous silicon on the active layer. An exposed portion of the drivingactive layer between the driving source electrode and the drainelectrode 52 and 54 acts as a channel in which electrons or holes passthrough. As the width to length ratio (W/L ratio) increases the oncurrent characteristic correspondingly improve. Therefore, to obtainthis advantage, the driving source electrode and drain electrode 52 and54 are formed as a plurality of finger shapes. At this time, the drivinggate electrode 34 under the driving source electrode and drain electrode52 and 54 is formed with an opening portion OP to minimize an overlapportion between the driving gate electrode 34 and the driving sourceelectrode and drain electrode 52 and 54. More specifically, thisstructure is utilized for reducing parasitic capacitance due to theoverlapping portion.

Hereinafter, it will be explained about the structure in accordance withthe driving gate electrode 34 and the driving source electrode and drainelectrode 52 and 54 referring to a specific numerical value.

When a channel length L defined as a distance between the driving sourceelectrode 52 and the driving drain electrode 54 is about 6 micrometersand an overlapping width between the driving gate electrode 34 and thedriving source electrode and drain electrode 52 and 54 is about 3micrometers, a minimum width of the driving gate electrode 34 should beabout 12 micrometers. Accordingly, the distance between the plurality ofdriving gate electrode 34 patterns adjacent to each other is about 6micrometers and the distance between the driving source electrode 52 andthe driving drain electrode 54 is about 6 micrometers. In addition, thewidths of the driving source electrode 52 and the driving drainelectrode 54 should be at least about 12 micrometers, respectively.Here, outermost portions of the driving source electrode 52 overlappingoutermost portions of the driving gate electrode 34 correspond to about6 micrometers.

Consequently, a width of the driving element T_(D) of FIG. 4 can becalculated as follows:The width of the driving source electrode 52: (6 micrometers×2)+12=24micrometersThe width of the driving drain electrode 54: 12 micrometers×2=24micrometersThe total channel length L of the driving element T _(D): 6micrometers×4=24 micrometersAccordingly, the width of the driving element T _(D): 24micrometers×3=72 micrometers

Consequently, when the driving source electrode and drain electrode 52and 54 are formed as having a finger shape and the driving gateelectrode 34 is formed with the opening portion OP, the width of thedriving element T_(D) may be about 72 micrometers. A driving elementT_(D) having a ring shape is suggested to enlarge the width to lengthratio (W/L ratio) as another example of the related art.

FIG. 5 is a schematic plan view showing a driving element of an OLEDaccording to a second example of the related art.

In FIG. 5, a driving element T_(D) includes a driving gate electrode 80,a driving semiconductor layer 82 over the driving gate electrode 80, adriving source electrode 83 and a driving drain electrode 86 spacedapart from the driving source electrode 83 on the driving semiconductorlayer 82. Here, the driving gate electrode 80 has a first ring shape,and the driving source electrode 83 has a second ring shape overlappingoutermost portion of the first ring shape of the driving gate electrode80. The driving source electrode 83 surrounds the driving drainelectrode 86 having an elliptical shape covering an opening portion OPof the driving gate electrode 80.

Also, this structure should be formed to obtain a large width to lengthratio (W/L ratio), so the ring-type driving element is manufactured asan excessive size in comparison to the switching element T_(S) (of FIG.3). Therefore, since a size of the driving element T_(D) occupies asignificant area in the pixel region P (of FIG. 3), the display regionis reduced. Consequently, it is difficult to manufacture an OLED havinghigh aperture ratio and high resolution.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an OLED and a methodof fabricating the same that substantially obviate one or more of theproblems due to limitations and disadvantages of the related art.

An object of the present invention is to provide an OLED having highaperture ratio and high resolution.

Another object of the present invention is to provide a method offabricating an OLED having high aperture ratio and high resolution byreducing the width of the driving element.

Another object of the present invention is to provide an OLED that canobtain enough storage capacitance without additional storagecapacitance.

Another object of the present invention is to provide a method offabricating an OLED that can obtain enough storage capacitance using anoverlap portion between the driving gate electrode and the drivingsource and drain electrodes without additional storage capacitancethrough forming a driving gate electrode corresponding to the drivingsource electrode and the driving drain electrode including an intervalbetween the driving source and drain electrodes.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, an organicelectroluminescent device includes a gate line on a substrate; a dataline crossing the gate line to define a pixel region; a power linecrossing one of the gate line and the data line; a switching elementincluding: a switching gate electrode connected to the gate line; aswitching source electrode connected to the data line; and a switchingdrain electrode spaced apart from the switching source electrode; and adriving element including: a driving source electrode connected to thepower line, the driving source electrode having a first driving sourceelectrode along a first direction and a plurality of second drivingsource electrodes extending from the first driving source electrodealong a second direction crossing the first direction; a driving drainelectrode spaced apart from the driving source electrode, the drivingdrain electrode having a first driving drain electrode along the firstdirection and a plurality of second driving drain electrodes extendingfrom the first driving drain electrode along the second direction,wherein the plurality of second driving source electrodes alternate withthe plurality of second driving drain electrodes; and a driving gateelectrode connected to the switching drain electrode, wherein thedriving source electrode and the driving drain electrode including aninterval therebetween corresponds to the driving gate electrode; and anorganic electroluminescent diode connected to the driving element.

In another aspect, an organic electroluminescent device includes: a gateline on a substrate; a data line crossing the gate line to define apixel region; a power line crossing one of the gate line and the dataline; a switching element including: a switching gate electrodeconnected to the gate line; a switching source electrode connected tothe data line; and a switching drain electrode spaced apart from theswitching source electrode; and a driving element including: a drivingsource electrode connected to the power line, the driving sourceelectrode having a ring shape; a driving drain electrode spaced apartfrom the driving source electrode and surrounded by the driving sourceelectrode; and a driving gate electrode connected to the switching drainelectrode, wherein the driving source electrode and the driving drainelectrode including an interval therebetween corresponds to the drivinggate electrode; and an organic electroluminescent diode connected to thedriving element.

In another aspect, a method of fabricating an organic electroluminescentdevice includes: preparing a substrate including a pixel region having aswitching region and a driving region; forming a gate line, a switchinggate electrode in the switching region and a driving gate electrode inthe driving region on the substrate, the driving gate electrode coveringthe driving region; forming a switching semiconductor layer over theswitching gate electrode and a driving semiconductor layer over thedriving semiconductor layer, respectively; forming a data line crossingthe gate line, a switching source electrode connected to the data line,a switching drain electrode spaced apart from the switching sourceelectrode, a driving source electrode having a first driving sourceelectrode along a first direction and a plurality of second drivingsource electrodes extending from the first driving source electrodealong a second direction crossing the first direction, and a drivingdrain electrode spaced apart from the driving source electrode, thedriving drain electrode having a first driving drain electrode along thefirst direction and a plurality of second driving drain electrodesextending from the first driving drain electrode along the seconddirection, and a driving gate electrode connected to the switching drainelectrode, wherein the plurality of second driving source electrodesalternate with the plurality of second driving drain electrodes, and thedriving source electrode and the driving drain electrode including aninterval therebetween corresponds to the driving gate electrode; forminga power line crossing one of the gate line and the data line, the powerline connected to the driving source electrode; and forming an organicelectroluminescent diode connected to the driving element.

In another aspect, a method of fabricating an organic electroluminescentdevice includes: preparing a substrate including a pixel region having aswitching region and a driving region; forming a gate line, a switchinggate electrode in the switching region and a driving gate electrode inthe driving region on the substrate, the driving gate electrode coveringthe driving region; forming a switching semiconductor layer over theswitching gate electrode and a driving semiconductor layer over thedriving semiconductor layer, respectively; forming a data line crossingthe gate line, a switching source electrode connected to the data line,a switching drain electrode spaced apart from the switching sourceelectrode, the driving source electrode having a ring shape, a drivingdrain electrode spaced apart from the driving source electrode andsurrounded by the driving source electrode, and a driving gate electrodeconnected to the switching drain electrode, wherein the driving sourceelectrode and the driving drain electrode including an intervaltherebetween corresponds to the driving gate electrode; forming a powerline crossing one of the gate line and the data line, the power lineconnected to the driving source electrode; and forming an organicelectroluminescent diode connected to the driving drain electrode.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a schematic cross-sectional view of an OLED according to arelated art.

FIG. 2 is an equivalent circuit diagram of the OLED according to therelated art.

FIG. 3 is a schematic cross-sectional view illustrating a switchingelement and a driving element including an amorphous TFT for one pixelregion of an OLED according to the related art.

FIG. 4 is a schematic plan view showing a driving element of an OLEDaccording to a first example of the related art.

FIG. 5 is a schematic plan view showing a driving element of an OLEDaccording to a second example of the related art.

FIG. 6 is an exemplary schematic expanded plan view showing an OLEDhaving a driving element according to the present invention.

FIGS. 7 to 9 are schematic plan views showing a driving element of anOLED according to first to third exemplary embodiments of the presentinvention, respectively.

FIG. 10 is a schematic plan view showing a driving element T_(D) havinga ring shape of an OLED according to a fourth exemplary embodiment ofthe present invention.

FIGS. 11A to 11F, 12A to 12F are schematic cross sectional views takenalong lines XI-XI and XII-XII in FIG. 6, respectively, illustrating afabricating process of a driving element of an OLED according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to the illustrated embodiments ofthe present invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

FIG. 6 is an exemplary schematic expanded plan view showing an OLEDhaving a driving element according to the present invention.

In FIG. 6, a gate line 104 is formed on a substrate 100 in a firstdirection, a data line 119 crosses the gate line 104 in a seconddirection to define a pixel region P, and a power line 132 is arrangedin parallel to the data line 119 and crosses the gate line 104. Aswitching element T_(S) adjacent to the pixel region P is connected tothe gate and data lines 104 and 119. A driving element T_(D) isconnected to the switching element T_(S). In addition, the switchingelement T_(S) includes a switching gate electrode 102, a switchingsemiconductor layer 110, switching source electrode and drain electrode120 and 121. The driving element T_(D) includes a driving gate electrode106, a driving semiconductor layer 114, a driving source electrode and adriving drain electrode 122 and 123. Specifically, the driving gateelectrode 106 is connected to the switching drain electrode 121, thedriving source electrode 122 is connected to the power line 132, and thedriving drain electrode 123 is connected to a first electrode 166 of anorganic electroluminescent diode D_(EL). The switching semiconductorlayer 110 and the driving semiconductor layer 114 may be formed ofamorphous silicon.

More specifically, the driving source electrode 122 includes a firstdriving source electrode 122 a along a first direction and a pluralityof second driving source electrodes 122 b extending from the firstdriving source electrode 122 a along a second direction crossing thefirst direction. The driving drain electrode 123 includes a firstdriving drain electrode 123 a along the first direction and a pluralityof second driving drain electrodes 123 b extending from the firstdriving drain electrode 123 a along the second direction, wherein theplurality of second driving source electrodes 122 b alternate with theplurality of second driving drain electrodes 123 b.

It is noted that the driving gate electrode 106 is connected to theswitching drain electrode 121, wherein the driving source electrode 122and the driving drain electrode 123 including an interval therebetweencorresponds to the driving gate electrode 106.

That is, since a width of the driving gate electrode 106 according tothe present invention is reduced in comparison with the width of thedriving gate electrode 34 (of FIG. 3) of the related art, an occupiedarea of the driving element T_(D) can be reduced with the same width tolength ratio (W/L ratio) of the related art. Therefore, when thisstructure is applied to the driving element T_(D) for OLED, it canobtain a high resolution.

Here, an overlap portion between the driving gate electrode 106 and thedriving source electrode and drain electrode 122 and 123 is utilized fora storage capacitance.

FIGS. 7 to 9 are schematic plan views showing a driving element of anOLED according to first to third exemplary embodiments of the presentinvention, respectively.

In FIG. 7, a driving element T_(D) includes a driving gate electrode106, a driving semiconductor layer 114 over the driving gate electrode106, a driving source electrode 122 on the driving semiconductor layer114 and a driving drain electrode 123 spaced apart from the drivingsource electrode 122 on the driving semiconductor layer 114, wherein thedriving gate electrode 106 has an area corresponding to the drivingdrain electrode 123 and the driving source electrode 122 including aninterval therebetween. In other words, the entire surface of the drivingsource electrode and drain electrode 122 and 123 overlap the drivinggate electrode 106. At this time, each of widths of the second drivingsource electrodes 122 b and the second driving drain electrodes 123 b isabout 6 micrometers as a minimum width and a channel length L defined asa distance between the second driving source electrodes 122 b and thesecond driving drain electrodes 123 b is about 6 micrometers.

As the above explained, the width of the driving element T_(D) accordingto the first embodiment of the present invention can be calculated asfollows:The width of the second driving source electrode 122b: 6micrometers×3=18 micrometersThe width of the driving drain electrode 123b: 6 micrometers×2=12micrometersThe total channel length L of the driving element T _(D): 6micrometers×4=24 micrometersAccordingly, the width of the driving element T _(D): (18+12+24)micrometers=54 micrometers

At this time, the channel length L is the same as the channel lengthaccording to the related art. In addition, the length of the drivingelement T_(D) is the same as the length thereof according to the relatedart. Accordingly, while the width of the driving gate electrode 106 issmaller than that of the related art, the distance and the width betweenthe second driving source electrode 122 b and the second driving drainelectrode 123 b can be maintained as that of the related art. Therefore,a high aperture ratio is obtained because the width of the drivingelement T_(D) is reduced. Further, the OLED having a high resolution canbe manufactured using the driving element according to the presentinvention since the overall size of the drive element can be reducedwithout sacrificing performance.

As shown in FIG. 7, outermost second driving source electrodes 122 b ofthe plurality of second driving source electrodes 122 b are in aperiphery with outermost second driving drain electrodes 123 b of theplurality of second driving drain electrodes 123 b, wherein each of theoutermost driving source electrodes 122 b has a first portionoverlapping the driving gate electrode 106 and a second portion notoverlapping the driving gate electrode 106.

In FIG. 8, the driving source electrode 222 is positioned at an insideof the driving gate electrode 206. Here, since the width of the drivinggate electrode 206 is at least about 6 micrometers, a negative effectdoes not occur.

In FIG. 9, a driving element T_(D), which provides an improved width tolength ratio (W/L ratio) as compared to the first and secondembodiments, is suggested as a highly improved characteristic of oncurrent due to the large width to length ratio (W/L ratio).

In particular, one of the outermost second driving source electrodes 322b of the plurality of second driving source electrodes 322 b and one ofthe outermost second driving drain electrodes 323 b of the plurality ofsecond driving drain electrodes 323 b are positioned at both outsides ofthe driving element T_(D), respectively. More specifically, each of theone of the outermost second driving source electrodes 322 b and the oneof the outermost second driving drain electrodes 323 b has a thirdportion overlapping the driving gate electrode 306 and a fourth portionnot overlapping the driving gate electrode 306.

Here, the second driving source electrodes 322 b and the second drivingdrain electrodes 323 b are three, respectively, thereby increasing thenumber of the channels therebetween.

For example, when the width between the second driving source electrode322 b and the second driving drain electrode 323 b is about 6micrometers and the channel length L between the second driving sourceelectrode 322 b and the second driving drain electrode 323 b is about 6micrometers, the width of the driving element T_(D) can be calculated asfollows:The width of the driving source electrode 322b: 6 micrometers×3=18micrometersThe width of the driving drain electrode 323b: 6 micrometers×3=18micrometersThe total channel length L of the driving element T _(D): 6micrometers×5=30 micrometersAccordingly, the width of the driving element T _(D): (18+18+30)micrometers=66 micrometers.

Although this structure according to the third embodiment provide alarger channel width than the structure of the first and secondembodiments, the width thereof is smaller than the width of the relatedart in accordance with increasing the number of the interval between thedriving source electrode and drain electrode 322 b and 323 b. Therefore,a much larger width to length ratio (W/L ratio) can be obtained comparedwith the related art while still reducing the overall size of thedriving element.

Accordingly, as on current of the driving element T_(D) increases,voltage stress applied to the driving element T_(D) can be minimized. Inaddition, since overlapping size between the driving gate electrode 306and the driving source electrode and drain electrode 322 b and 323 b islarger than the overlapping size according to the related art, enoughstorage capacitance can be obtained.

FIG. 10 is a schematic plan view showing a driving element T_(D) havinga ring shape of an OLED according to a fourth exemplary embodiment ofthe present invention.

In FIG. 10, a driving element T_(D) includes a driving gate electrode406, a driving source electrode 422 having a ring shape, and a drivingdrain electrode 423 spaced apart from the driving source electrode 422and surrounded by the driving source electrode 422, wherein the drivingsource electrode 422 and the driving drain electrode 423 including aninterval therebetween corresponds to the driving gate electrode 406.

Also, this embodiment has an advantage that a much larger storagecapacitance can be obtained due to the structure of the driving gateelectrode 406.

FIGS. 11A to 11F, 12A to 12F are schematic cross sectional views takenalong lines XI-XI and XII-XII in FIG. 6, respectively, illustrating afabricating process of a driving element of an OLED according to anembodiment of the present invention.

In FIGS. 11A and 12A, a pixel region P, a switching region S and adriving region D are defined in a first substrate 100. A switching gateelectrode 102 and a driving gate electrode 106 are formed on the firstsubstrate 100 by depositing and patterning a metal layer such asaluminum (Al), Al alloy, tungsten (W), copper (Cu), molybdenum (Mo),titanium (Ti) or the like. Although not shown, the switching gateelectrode 102 is connected to a gate line which is formed on the firstsubstrate 100 in a first direction.

It is noted that the driving gate electrode 106 is formed to correspondto a driving source electrode and a driving drain electrode that will beformed later.

In FIGS. 11B and 12B, a gate-insulating layer 108 is formed over thefirst substrate 100 having the switching gate electrode 102 and thedriving gate electrode 106. The gate-insulating layer 108 is formed bydepositing an inorganic insulating material such as silicon nitride(SiN_(x)) or silicon oxide (SiO₂). A switching semiconductor layer 110and a driving semiconductor layer 114 are formed over the switching gateelectrode 102 and driving gate electrode 106, respectively, bysequentially depositing and patterning intrinsic amorphous silicon anddoped amorphous silicon. Thus, the gate-insulating layer 108 is formedbetween the switching and driving semiconductor layers 110 and 114 andthe switching and driving gate electrodes 102 and 106, respectively. Theswitching semiconductor layer 110 includes a switching active layer 109and a switching ohmic contact layer 112. Likewise, the drivingsemiconductor layer 114 includes a driving active layer 113 and adriving ohmic contact layer 116. In addition, the gate-insulating layer108 has a gate contact hole 118 that exposes a portion of the drivinggate electrode 106 (FIG. 11B).

In FIGS. 11C and 12C, switching source electrode and drain electrode 120and 121, and driving source electrode and drain electrode 122 and 123are formed on the switching semiconductor layer 110 and drivingsemiconductor layer 114, respectively, by depositing and patterning ametal layer. Specifically, the switching source electrode and drainelectrode 120 and 121 contact the switching ohmic contact layer 112, andthe driving source electrode and drain electrode 122 and 123 contact thedriving ohmic contact layer 116.

The driving source electrode 122 includes a first driving sourceelectrode 122 a along the first direction (not shown in FIG. 12C) and aplurality of second driving source electrodes 122 b extending from thefirst driving source electrode 122 a along the second direction crossingthe first direction. The driving drain electrode 123 is spaced apartfrom the driving source electrode 122, the driving drain electrode 123including a first driving drain electrode 123 a along the firstdirection (not shown in FIG. 12C) and a plurality of second drivingdrain electrodes 123 b extending from the first driving drain electrode123 a along the second direction, wherein the plurality of seconddriving source electrodes 122 b alternate with the plurality of seconddriving drain electrodes 123 b, and the driving source electrode 122 andthe driving drain electrode 123 including an interval therebetweencorresponds to the driving gate electrode 106. Here, the driving gateelectrode 106 is connected to the switching drain electrode 121 throughthe gate contact hole 118.

Next, a portion of the switching and driving ohmic contact layers 112and 116, respectively, between the switching and driving sourceelectrodes 120 and 122 and the switching and driving drain electrodes121 and 123 are removed to expose a portion of the switching and drivingactive layer 109 and 113 under the portion of switching and drivingohmic contact layers 112 and 116, respectively.

In FIGS. 11D and 12D, a first passivation layer 124 is formed over thefirst substrate 100 including the switching source electrode and drainelectrode 120 and 121, and the driving source electrode and drainelectrode 122 and 123. The first passivation layer 124 has a firstcontact hole 128 that exposes an edge portion of the driving sourceelectrode 122.

In FIGS. 11E and 12E, a power line 132 (FIG. 12E) is formed bydepositing and patterning a conductive layer and is connected to thedriving source electrode 122 through the first contact hole 128.However, power line 132 may be formed simultaneously with gate electrode106.

In FIGS. 11F and 12F, a second passivation layer 134 is formed bydepositing an inorganic insulating material such as silicon nitride(SiNx) or silicon oxide (SiO₂) or by coating an organic insulatingmaterial such as benzocylcobutene (BCB) or acrylic resin. Although notshown in FIGS. 11F and 12F, the second passivation layer 134 may have asecond contact hole through which the driving drain electrode 123 isconnected to the first electrode 166 (of FIG. 6).

Although not shown, an organic electroluminescent diode is connected tothe driving element T_(D). More specifically, the organicelectroluminescent diode includes a first electrode connected to thedriving drain electrode 123, an organic electroluminescent layer on thefirst electrode and a second electrode on the organic electroluminescentlayer.

When the first electrode functions as a cathode, it includes atransparent conductive material having a high work function. When thesecond electrode functions as an anode, the second electrode may be madeof an opaque (non-transparent) conductive material having a small workfunction.

Although the minimum width between the driving source electrode and thedriving drain electrode is about 6 micrometers according to theembodiments of the present invention, the width is not limited to 6micrometers. For example, the width therebetween may be more than about6 micrometers.

When the driving element of the OLED according to the present inventionincludes the driving gate electrode corresponding to the driving sourceelectrode and the driving drain electrode including the intervaltherebetween, the width of the driving gate electrode can be reducedwithout changing the width to length ratio (W/L). Therefore, the OLEDusing the driving element can achieve as a high resolution.

In addition, when the width of the driving gate electrode is fixed, thenumber of the second driving source and drain electrodes can beincreased to improve the on current characteristics so that stabledriving features can be obtained.

Further, the increase in the overlap area between the driving gateelectrode and the driving source and drain electrodes can be utilized asstorage capacitance. Consequently, additional storage capacitance is nolonger required and productivity yield can be improved.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the OLED and a method offabricating the same of the present invention without departing from thespirit or scope of the invention. Thus, it is intended that the presentinvention cover the modifications and variations of this inventionprovided they come within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. An organic electroluminescent device, comprising: a gate line on a substrate; a data line crossing the gate line to define a pixel region; a power line crossing one of the gate line and the data line; a switching element; a driving element including: a driving gate electrode connected to the switching element, the driving gate electrode formed uniformly on the substrate; a gate-insulating layer on the driving gate electrode; a driving semiconductor layer on the gate-insulating layer; a driving source electrode connected to the power line, the driving source electrode having a first driving source electrode along a first direction and a plurality of second driving source electrodes extending from the first driving source electrode along a second direction crossing the first direction; a driving drain electrode spaced apart from the driving source electrode, the driving drain electrode having a first driving drain electrode along the first direction and a plurality of second driving drain electrodes extending from the first driving drain electrode along the second direction, wherein the plurality of second driving source electrodes alternate with the plurality of second driving drain electrodes, wherein the driving source electrode and the driving drain electrode including an interval therebetween are facing the driving gate electrode, wherein the driving semiconductor layer on the gate-insulating layer completely covers four sides of the driving gate electrode under the gate-insulating layer; and an organic electroluminescent diode connected to the driving element, wherein one of outermost second driving source electrodes of the plurality of second driving source electrodes and one of outermost second driving drain electrodes of the plurality of second driving drain electrodes are positioned at opposing outermost edges of the driving element, respectively.
 2. The device according to claim 1, wherein each of the one of outermost second driving source electrodes and the one of the outermost second driving drain electrodes has a third portion overlapping the driving gate electrode and a fourth portion not overlapping the driving gate electrode.
 3. A method of fabricating an organic electroluminescent device, comprising: preparing a substrate including a pixel region having a switching region and a driving region; forming a gate line, a switching gate electrode in the switching region, and a driving gate electrode in the driving region on the substrate, wherein the driving gate electrode is formed uniformly on the substrate; forming a gate-insulating layer on the switching gate electrode and the driving gate electrode; forming a switching semiconductor layer on the gate-insulating layer over the switching gate electrode and a driving semiconductor layer on the gate-insulating layer over the driving gate electrode; forming a data line crossing the gate line, a switching source electrode connected to the data line, a switching drain electrode spaced apart from the switching source electrode and connected to the driving gate electrode, a driving source electrode having a first driving source electrode along a first direction and a plurality of second driving source electrodes extending from the first driving source electrode along a second direction crossing the first direction, and a driving drain electrode spaced apart from the driving source electrode, the driving drain electrode having a first driving drain electrode along the first direction and a plurality of second driving drain electrodes extending from the first driving drain electrode along the second direction, wherein the plurality of second driving source electrodes alternate with the plurality of second driving drain electrodes, and the driving source electrode and the driving drain electrode including an interval therebetween are facing the driving gate electrode, and wherein the driving semiconductor layer on the gate-insulating layer completely covers four sides of the driving gate electrode under the gate-insulating layer; forming a power line crossing one of the gate line and the data line, the power line connected to the driving source electrode; and forming an organic electroluminescent diode connected to the driving element, wherein one of outermost second driving source electrodes of the plurality of second driving source electrodes and one of outermost second driving drain electrodes of the plurality of second driving drain electrodes are formed to position at both outsides of the driving element, respectively.
 4. The method according to claim 3, wherein each of the one of outermost second driving source electrodes and the one of outermost second driving drain electrodes is formed to have a third portion overlapping the driving gate electrode and a fourth portion not overlapping the driving gate electrode. 